1. Field of the Invention
This invention relates to an interlace recording apparatus and method. More specifically, this invention relates to an interlace recording apparatus and method which perform recording using an ink jet recording head.
2. Description of the Related Art
Recently, since demands for quality improvement of a recorded image are increasing, attempts have been made to raise recording resolution in a printer. For example, in the recording apparatus which scans an ink jet recording head in the main scanning direction and performs image recording by discharging ink on a recording medium during the scanning, attempts have been made to improve recording resolution with regard to the main scanning direction as follows.
When ink is discharged from a nozzle of the recording head corresponding to a position of a carriage, which carries the recording head and moves back and forth in the direction of the main scanning, if resolution of carriage position detection is doubled, an additional dot can be formed between dots formed by conventional ink discharge on the recording medium. This modification can be performed relatively easily. For example, when recording resolution with regard to the main scanning direction is 360 dpi (dot per inch), if a head controller is modified to be able to generate a drive timing signal of the recording elements provided with the recording head in between adjacent dots, it is possible to turn recording resolution with regard to the main scanning direction into 720 dpi.
Attempts have been made to improve recording resolution with regard to the sub-scanning direction, which is a feed direction of a recording medium, as follows.
One attempt is, for example, to make a recording head having a recording resolution of 720 dpi by making nozzles of the recording head arranged in the direction of sub-scanning themselves minute and at an increased nozzle density. However, a technical barrier is high with respect to construction accuracy of the recording head nozzles in this case, so it is difficult to realize.
Another attempt is to not alter the nozzle resolution or density (for example, 360 dpi), but rather to improve the resolution in the sub-scanning direction, for example, by refining resolution of a line feed control of the recording medium. In order to change a recording resolution of 360 dpi into a recording resolution of 720 dpi, first recording is performed at a standard (normal) recording position at the recording resolution of 360 dpi with one line of dots being formed for each nozzle of the recording head, and next recording is performed at the middle position between adjacent lines of dots in one main scan. In other words, interlace recording is performed.
FIG. 8 is a block diagram showing structure of a conventional head controller which controls interlace recording. The controller includes a control circuit of a printer using an ink jet recording head and controls the recording head. By controlling interlace recording using the controller, recording can be effected at a recording resolution of 720 dpi using the recording head of which the nozzle recording resolution is 360 dpi. In the following, in order to make the explanation simple, the number (N) of nozzles of the recording head is 16.
In FIG. 8, reference numeral 171 is a mask register which stores a matrix of a mask used in multi-pass recording control to reduce recording unevenness (banding). With regard to the multi-pass recording control, such is described in detail in Japanese Laid-Open Patent Application No. 5-31922. The description of multi-pass recording in that Japanese document is incorporated herein by reference. Reference numeral 172 is a mask address counter indicating an address of the mask register 171, and reference numeral 173 is a mask circuit operating the logical product of 16 bits of recording data and 16 bits of mask data. Reference numeral 174 is a parallel/serial conversion circuit latching output from the mask circuit 173 and transferring 16 bits of recording data into a head driver serially, reference numeral 175 is a transfer timing controller controlling transfer timing of the parallel/serial conversion circuit 174, and reference numeral 176 is a heat pulse generating circuit.
A control signal and recording data are input to the head controller of such structure from a CPU (not shown), which is additional structure of the control circuit, as well as a carriage position detecting section and a RAM/DMA controller for performing transfer control of the recording data. First of all, when the recording timing pulse of the main scanning direction input from the carriage position detecting section is detected, the mask address counter 172 counts up. In a case where recording is performed during the return of the recording head, it counts down. The mask data is output from an address of the mask register 171 which is determined by a count value of the counter 172, and recording data is transferred to the mask circuit 173 from the RAM/DMA controller. The mask circuit 173 operates the logical product of the mask data and recording data, and the logical operation result is latched by the parallel/serial conversion circuit 174.
After that, recording data is serially transferred from the parallel/serial conversion circuit 174 to the head driver according to a transfer clock pulse supplied from the transfer timing controller 175. By the heat pulse generating circuit 176 sending a heat signal to the head driver, electric current flows to the recording elements of the recording head and then the heaters of the recording elements are heated at the time of current input following the recording timing pulse of the main scanning direction.
FIGS. 9A and 9B are illustrations showing a condition of interlace recording at a recording resolution of 720 dpi using a recording head having a nozzle recording resolution of 360 dpi and having 16 nozzles in the sub-scanning direction. In FIGS. 9A and 9B, N15, N14, N13, . . . , N0 show 16 nozzles, respectively. In the interlace recording, while moving the recording head in the main scanning direction at a standard recording position, recording is first performed at recording resolution of 360 dpi. In other words, a start address of a RAM which stores recording data used to record at a standard recording position is set in the DMA/RAM controller, the carriage carrying the recording head is moved by driving a carriage motor and one main scan line (16 nozzle width) of recording is performed with one line of dots corresponding to each of the 16 nozzles. By the recording, the dots shown as white circles are recorded as shown in FIG. 9A.
Secondly, the recording medium is fed by 1/720 inch in the sub-scanning direction by driving a line feed motor. A start address of the RAM which stores recording data used to record between adjacent lines of dots recorded previously is set in the DMA/RAM controller, the carriage carrying the recording head is moved by driving the carriage motor and one line (16 nozzle width) of recording is performed. By the recording, the dots shown as cross-hatched circles are recorded as shown in FIG. 9B.
By recording two times as mentioned above, image recording having one line of a 32 dot width (16 nozzle width), at a resolution of 720 dpi is completed in the sub scanning direction. FIGS. 10A and 10B are illustrations showing one example of the recording data arranged in the RAM within a control circuit in the case of interlace recording mentioned above. FIG. 10A shows the image data prepared for the recording shown in FIG. 9A, and FIG. 10B shows the image data prepared for the recording shown in FIG. 9B. In addition, the numerical values shown in FIGS. 10A and 10B correspond to a nozzle number of the 16 nozzles. For example, "9" corresponds to the data to be recorded by nozzle number N9. In this way, the conventional interlace recording requires one area (recording buffer) storing the recording data to be recorded at the standard recording positions and another area storing the recording data to be recorded in between the standard positions (hereinafter, called interlace recording position) within the RAM.
In the prior art the following problems arise. In conventional interlace recording, the CPU of the control circuit carries out a control program to develop the recording data which are the recording data to be recorded at the standard recording positions (for example, at the 360 dpi positions) and the recording data to be recorded at the interlace recording positions (for example, at the 720 dpi positions) and to store them separately in the RAM. The load on the CPU increases because of this process, so recording performance falls as a result.
Moreover, when recording is performed at a recording resolution of 720 dpi with regard to both the main scanning direction and the sub-scanning direction, four times the capacity of the recording buffer is required in the prior art mentioned above. For this reason, in the prior art the size of the RAM has to be increased and drastic modification of the circuit board is required resulting in a rise in the production cost.